The earliest film of Kubrick's that I've seen is The Killing
, which is quite good, but not great. The Blu-Ray also has Killer's Kiss
on it, but I haven't watched it yet.
I have also seen Dr. Strangelove, or How I Learned to Stop Worrying and Love the Bomb
, 2001: A Space Odyssey
, A Clockwork Orange
, The Shining
, and Full Metal Jacket
. I'd say all but one of those films is great, but I'll wait until you get that far.